# Deny non-local messages with no Message-ID, or no Date
  #
  # Note that some specialized MTAs, such as certain mailing list
  # servers, do not automatically generate a Message-ID for bounces.
  # Thus, we add the check for a non-empty sender.
  #
  deny
    message     = Your message does not conform to RFC2822 standard
    log_message = missing header lines
    !hosts      = +relay_from_hosts
    !senders    = : postmaster@*
    condition   = ${if or {{!def:h_Message-ID:}\
                           {!def:h_Date:}\
                           {!def:h_Subject:}} {true}{false}}